Digital data radio systems, such as, but not limited to, those employed in electricity, gas, and water utility automated meter reading (AMR), industrial supervisory control and data acquisition (SCADA), building automation, residential home automation, and other wireless data networks, often employ spread-spectrum radio technology to reduce communications problems caused by interference, and for other reasons.
One type of spread-spectrum radio technology is frequency-hopping spread spectrum (FHSS). A frequency-hopping spread spectrum radio transmitter employs a single carrier frequency at any given moment, but it employs a plurality of carrier frequencies over time and changes the carrier frequency often. The frequency channels and hopping sequence that the transmitter employs may be random, pseudo-random, or predetermined. Hops in the sequence may range within known or unknown upper and lower bounds.
A single-channel radio receiver is a radio receiver capable of tuning to only one carrier frequency at a time. A single-channel radio receiver may be fixed-frequency, meaning that the carrier frequency cannot be changed, or it may be frequency-agile, meaning that the carrier frequency can be quickly and easily changed through software or firmware without requiring any physical changes to the receiver's circuitry.
Reliable reception of the radio signals emitted by a frequency-hopping spread spectrum transmitter using a single-channel receiver requires the receiver controller to adjust the receiver's carrier frequency in synchrony with the transmitter's carrier frequency changes. Use of this frequency selection (a.k.a. tuning or hopping) technique has generally required the controller to employ the same frequency-hopping sequence and channels as the transmitter.
A single channel receiver, for that reason, has not been well-suited to receiving signals emitted by a transmitter employing a random, pseudo-random, or otherwise unknown frequency-hopping pattern and channel set. Because such information cannot be known by the receiver controller, the receiver cannot intentionally tune to the correct transmission frequency. A common technique to deal with this has been to tune the receiver to a fixed frequency and wait for the transmitter's hopping sequence to intersect it, to employ a blind scan covering a large frequency range, or to hop randomly and arbitrarily. These result in very infrequent reception of the signals of interest.
Another technique is to increase the receiver's passband to the point where the section of radio spectrum received is significantly larger than the bandwidth of the signals of interest (reducing the receiver's selectivity), with the undesirable side effect that the receiver's signal-to-noise ratio decreases to an unsatisfactory level.
All such well-known techniques often result in the receiver's failure to receive the desired signals with sufficient sensitivity or regularity. The problem is exacerbated when the upper or lower bounds of the frequency-hopping range are not known or vary from transmitter to transmitter or from time to time.
A multi-channel radio receiver is customarily used to overcome this problem at the expense of additional cost and complexity when compared to a single-channel receiver. A multi-channel radio receiver is a receiver capable of discerning signals on more than one carrier frequency simultaneously while maintaining a high level of channel selectivity. Such a receiver is generally either a composite of multiple single-channel receivers or utilizes digital signal processing (DSP) technology to mathematically extract multiple channels simultaneously from a broadband signal.